1. Field of the Invention
The present invention relates to a tank cap having a pressure regulating valve to regulate the inner pressure of a tank.
2. Description of the Related Art
One typical example of tank caps is a fuel cap that opens and closes a fill port of a fuel tank for automobiles (see, for example, JP No. 10-278957A). The fuel cap includes a pressure regulating valve to regulate the inner pressure of the fuel tank. The pressure regulating valve includes a valve plug and a spring that applies a pressing force to the valve plug. One end of the spring is supported to press the valve plug, while the other end of the spring is fixed to an inner cover of the fuel cap. The inner cover is a resin plate with a connection hole that communicates a valve chest with the atmosphere, and is fixed to an upper end opening of a casing of the fuel cap by, for example, ultrasonic welding technique.
The ultrasonic welding technique, however, has limitation on the welding strength of the inner cover. The ultrasonic welding technique often causes weld flash, which may be invaded into the pressure regulating valve and malfunction the pressure regulating valve.
Another known technique uses a plate member that locks one end of the spring. Press engagement of locking elements provided on the plate member with the casing of the fuel cap fixes the plate member (see JP No. 1-137863A).
The large engagement force of the locking elements of the plate member with the casing of the fuel cap undesirably lowers the assembly efficiency. The small engagement force, however, lowers the assembly strength of the plate member and the casing. Namely it is difficult to make the high assembly efficiency compatible with the high assembly strength.